Federal authorities arrested three Los Angeles area residents Wednesday for allegedly running a multi-million dollar 'pay to stay' visa fraud scheme that let foreign nationals stay in the U.S. by "attending" vocational schools without attending classes.

The four schools were based in the L.A. area but almost all the students lived elsewhere. The investigation found that many were living as far away as Hawaii, Texas and Washington. When investigators visited one of the schools, they found only one student attending a class when records indicated the college had 300 students.

According to the 21-count indictment, the three defendants collected more than $6 million in tuition payments from citizens of South Korea, China and other nations.

Defendant Hee Sun Shim, a.k.a Leo Shim , 51, who allegedly owned and managed the schools, was arrested near his Beverly Hills home by ICE agents. Also arrested Wednesday were two employees who allegedly assisted with operation and management of the schools, Hyung Chan Moon, a.k.a. Steve Moon, 39, and Eun Young Choi, a.ka. Jamie Choi, 35, both of Los Angeles.

The indictment charges Shim, Moon and Choi with conspiring to commit immigration fraud. Shim is charged with 13 counts of use or possession of an immigration document procured by fraud, and Moon and Choi are each charged with one count of the same offense. Shim is charged with three counts of encouraging illegal residence, as well as two counts of money laundering.

Each immigration fraud charge can carry up to 10 years in prison while the maximum sentence for money laundering is 20 years behind bars.

"Given the implications for national security and public safety, we will move aggressively to target individuals who compromise the integrity of our nation's immigration system out of greed and self-interest," Claude Arnold, special agent in charge for HSI Los Angeles said in a statement. "Simply put, those who exploit the benefits of the student visa program can expect to get a lesson in criminal justice."

Three of the schools -- Prodee University, Walter Jay M.D. Institute, and the American College of Forensic Studies (ACFS) -- are in the Koreatown section of L.A., while a fourth school, the Likie Fashion and Technology College, is located in Alhambra.

Federal authorities began their investigation in 2011 with unnannounced visits to Prodee's Wilshire Blvd. campus and ACFS. At Prodee, agents found three students attending a single class, while at ACFS there was only one student in one class. At the time, records showed the schools had enrolled 1200 students.

As the investigation continued, authorities found that Shim and Choi were allegedly creating bogus student records, including transcripts, for some of the students. In exchange for a form that makes sudents eligible for an F-1 visa, a student would make "tuition" payments of as much as $1,800 to "enroll" for six months in one of the schools, according to the indictment.

In cases where students were in the country for longer periods of time, authorities allege Shim would transfer a purported student from one school to another to avoid arousing the suspicion of immigration authorities.

Last year, the founder and former president of a Bay Area university was sentenced to more than16 years in federal prison in connection with a student visa fraud scheme that generated nearly $6 million in profits.

Also in 2014, the former head of an English language school in Duluth, Georgia, was sentenced in a scheme in which he allegedly worked with Korean bar owners to enroll women in the school with the understanding that they would not attend classes as required but would instead work in the bars.